The proposed fellowship project will focus on optimizing an in vitro model system to test novel Huntington's disease (HD) therapeutics, creating a library of gene modification strategies aimed at silencing or correcting specifically th mutant gene in HD, and demonstrating robust and durable knockdown of HD-related cellular deficits using gene modification. The first of these three specific aims will be accomplished by validating a novel cellular model in which HD related dysfunction can be measured in a cost-effective, robust, and reproducible manner. This will be done by confirming mutant-allele-dependent deficits in fibroblast cultures isolated from HD patients. The second goal will be accomplished by first identifying specific target sites within the mutant allele for which gene modifying strategies can be developed. This will be done by identifying single nucleotide polymorphisms in the mutant allele that exist in greater than 40% of the Huntington's population and creating a library of transcription activator-like effectors (TALE) that can identify and silene or correct the mutant gene. By targeting single nucleotide polymorphisms that exist in the mutant allele, it will be possible in future studies to choose a patient-specific TALE from our library that will specifically suppress the mutant allele in that individual either independently o acting synergistically with a combination of TALEs suited for that persons genome. The results from this proposal will help further the knowledge of personalized treatment for patients suffering from HD and will help disseminate the function of the huntingtin gene in patient-specific human cell lines. A working library of TALE will be created that theoretically covers over 40% of the HD population and knowledge from this exploratory study can be applied to create personalized therapeutics for the vast majority of HD patients. This fellowship is in line with the mission of the National Institute of Neurological Disorders and Stroke as it will further the knowledge of the function of huntingtin gene, protein aggregation and misfolding, and the extent to which mitochondrial dysfunction occurs in a mutant allele- length dependent manner and the ability of these deficits to be corrected with gene modification. This fellowship will be conducted under the expert training of two senior principle investigators with extensive knowledge of genome targeting, gene therapy, and the development of therapeutic interventions for clinical trials. The work will be performed in collaboration between the two labs with direct supervision from the sponsor and co-sponsor. The fellowship will greatly enhance the knowledge base for personalized therapies, through careful examination of patient- specific gene modifiers for individuals suffering from genetic disorders.